1. Field of the Invention
This invention relates to a selective gas-permeable composite membrane suitable for use in gas separation. When the composite membrane is used, intended gas, such as an oxygen gas, can be selectively separated from mixtures.
2. Description of the Prior Art
In recent years, many techniques for separating an intended gas from a gas mixture for concentration have been in use. For instance, several types of separation membranes have been employed for concentration of oxygen from air, for separation and concentration of hydrogen for industrial applications and for recovery of carbon dioxide. Oxygen enriching membranes which are especially used to concentrate oxygen in air have wide utility in various industrial fields.
Currently employed oxygen-enriching membranes which are used to treat the air are, in most cases, made of polyorganosiloxanes. The inherent oxygen permeability of the organopolysiloxane membranes is generally in the order of 10.sup.-1 cc/cm.sup.2 .multidot.sec.multidot.atm. Although this type of membrane has relatively high gas permeability, the separation ratio between oxygen and nitrogen is relative small, i.e., up to 2, so that the oxygen concentration in final enriched air is up to about 30%.
Another type of oxygen-enriching membrane is known for its application in medical services. In this case, the separation ratio between oxygen and nitrogen in air is about 3.about.4 and the resultant enriched air contains approximately 40% of oxygen. However, this membrane can treat only a small amount of a gas mixture. For instance, with polyolefin films, the permeability of oxygen is as small as 10.sup.-2 .about.10.sup.-3 cc/cm.sup.2 .multidot.sec.multidot.atm. Wide utility has been expected for a membrane which has a large permeation rate and high selectivity. Thus, there is a strong demand for the development of high performance membranes.